Diamines play a unique part in shaping the characteristics and structure of polyurethanes. The polyurethane extending, crosslinking and curing effects are typically unpredictable in a manner similar to catalysis in the hydrocarbon catalytic polymerization art. Polyurethane compositions obtained by curing liquid isocyanato-terminated prepolymers with diamines are finding increased use in diverse applications requiring castable elastomers. Because of their abrasion resistance, they are frequently used as coatings on surfaces subject to mechanical wear. The use of polyurethanes has been somewhat restricted due to difficulties encountered in the curing process with the diamine curing agents currently available. One major difficulty with a most popular diamine currently available is that it is potentially toxic.
The most commonly used amine curing agents are hindered or substituted aromatic diamines of which 3,3'-dichlorobenzidine and 4,4'-methylene-bis-(2-chloroaniline), also known as MOCA, are representative. MOCA is an effective and well known extender or curative for polyurethanes. Unfortunately, the material is believed to be carcinogenic. This invention describes the preparation of two materials which have shown negative Ames tests but still cured polyurethanes in a manner similar to MOCA.
U.S. Pat. No. 3,640,955 discloses high molecular weight polyurethanes based on condensing di- or trinuclear N,N'-dialkyldiamines with bifunctional carbonic acid derivatives. More specifically, this patent discloses a polyurethane resin in which all nitrogen atoms are substituted by methyl groups or ethyl groups. The U.S. Pat. No. 3,640,955 fails to disclose or appreciate that the curatives of this invention can provide polyurethanes of excellent physical properties without the dangers attendant with curatives such as MOCA.
U.S. Pat. No. 3,734,896 relates to a process and products resulting from curing polyisocyanate prepolymers with either HCN, mixtures of HCN and one or more polyisocyanates with polycyanoformamides, all in the presence of a suitable catalyst, such as CN-- and tertiary amines.
U.S. Pat. No. 3,897,400 discloses cured polyurethanes prepared by reacting 4,4'-diaminodiphenylsulfide with a mixture of organic polyisocyanate and polymeric polyol containing an excess of said polyisocyanate or with a prepolymer of said polyisocyanate and polymeric polyol.
U.S. Pat. No. 3,905,944 discloses the use of 4,4'-diaminodiphenyldisulfide as a curative for polyurethane reaction mixtures.
U.S. Pat. No. 3,926,919 discloses polyurethane compositions cured by reacting 2,2'-diaminodiphenyldisulfide with an isocyanate terminated polyol.
The use of aromatic diamines such as MOCA is well known as is the use of 4,4'-methylenedianiline, some times known as MDA. For typical commercial applications, however, the MDA reacts too fast and MOCA is a suspected carcinogen.
In accordance with this invention, it has been discovered that substitution of a single aromatic diamine of the structural formula: ##STR1## for MOCA or MDA curatives provides cured polyurethane compositions which possess excellent physical properties. The curative of this invention may be used with isocyanate terminated polyol, polyurethaneprepolymers and do not need a catalyst at room temperature to provide a reaction rate suitable for most commercial applications.